There is little data regarding the action of HLH proteins in the skin. I have used RT-PCR Northern blotting analysis, immunocytochemistry (ICC) and in situ hybridisation (ISH) to determine the expression profiles of Id1, Id2, Id3 and Id4 and the Class A factors E2A, E2-2 and HEB mRNAs and proteins during human keratinocyte differentiation both <I>in vivo</I> and in monolayer and organotype <I>in vitro</I> differentiation culture models, and in the human anagen hair follicle, the rat hair follicle growth cycle, and the human sebaceous gland and eccrine sweat gland. Preliminary RT-PCR analysis determined that the Class A factors, E2A, E2-2 and HEB and Id1, Id2 and Id3, and to a very limited extent Id4 mRNAs, were expressed by the epidermis and skin appendages. Northern blotting analysis demonstrated that Ca<SUP>2+</SUP> induced cell cycle withdrawal and differentiation of primary human keratinocytes, determined by an up regulation of p21<SUP>cip1</SUP> and involucrin mRNA expression, was inversely correlated with Id1, Id2 and Id3 mRNA expression. ICC and ISH analysis of human and rat epidermis confirmed Id protein and mRNA expression in the most proliferative layers of the epidermis. The sub-cellular localisation of Id1 protein was predominantly cytoplasmic, whereas that of Id2 and Id3 proteins was predominantly nuclear. Interestingly, a sub-population of supra-basal, post-mitotic keratinocytes also expressed Id1, Id2 and Id3 proteins in which the sub-cellular localisation of each was predominantly nuclear. Supra-basal Id expressing keratinocytes were often seen arranged in stacks extending from the basal layer to the confirmed layers and these cells may be post-mitotic keratinocytes with maintained capacity to re-enter the cell cycle, and may delineate epidermal proliferative units.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:598622 |
| Date | January 2001 |
| Creators | Down, G. |
| Publisher | University of Cambridge |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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